1. Field of the Invention
The present application relates to the field of thermoelectric power generation, and more particularly to systems for improving the generation of power from thermoelectrics, particularly in the situation where there are limitations in the system on the temperature differential across the thermoelectric.
2. Description of the Related Art
Thermoelectrics are solid state devices that operate to become cold on one side and hot on the other side when electrical current passes through. They can also generate power by maintaining a temperature differential across the thermoelectric. Under many operating conditions, however, thermoelectric power generators are exposed to a combination of changing heat fluxes, hot side heat source temperatures, cold side temperatures, and other variable conditions. In addition, the device properties, such as TE thermal conductance, figure of merit Z, heat exchanger performance all have a range that can combine to, in general, reduce device performance. As a result, performance varies and operation at a predetermined set point can lead to performance degradation compared to the design.
Any process that consumes energy that is not 100% efficient generates waste energy, often in the form of heat. For example, engines generate a substantial amount of waste heat, representing inefficiency in the engine. Various ways to attempt to capture and use some of this waste heat have been considered in order to improve the efficiency of any type of engine, such as the engine in automobiles. Placing thermoelectrics on the exhaust system of an automobile has been contemplated (See U.S. Pat. No. 6,986,247 entitled Thermoelectric Catalytic Power Generator with Preheat). However, the exhaust system varies greatly in temperatures and heat flux. Thus, because a thermoelectric generator is typically designed to operate effectively over a small range of hot side temperatures, using exhaust for the hot side of a thermoelectric generator is suboptimal. In addition, a logical cold side coolant for a thermoelectric generator linked to an engine system is the engine coolant already provided. However, the coolant needs to be maintained at a fairly hot temperature for efficient engine operation. Thus, using the existing coolant limits the temperature gradient that can be established across the thermoelectric generator, thereby limiting effective waste heat recovery.